The half-life of strontium-90 is 28 years. How long will it take a 50-mg sample decay to a mass of 32-mg?

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Because the half-life is 28 years, the number of moles halves every 28 years.so let u = 28 years.50 (Original) * .5^u (halves every U years) = 32 (ending sample).5^u = 32/50using change of base we have:u = log(32/50)/log(.5)= 0.643856190.64385619* 28 years = 18.0279733 yearsHope this helps!